One type of flexible, resilient valve is a self-closing, slit-type valve mounted by a fitment to a port of a fluent substance container or other source of fluent substance. Such valves have a slit or slits which define a normally closed orifice that opens to permit flow therethrough in response to an increased pressure differential across the valve (e.g., resulting from an increased pressure within the container when the container is squeezed, or from a reduced external ambient pressure compared to the pressure within the container). Such valves are typically designed so that they automatically close to shut off flow therethrough upon a reduction of the pressure differential across the valve.
Designs of such valves and of fitments using such valves are illustrated in the U.S. Pat. Nos. 5,271,732, 5,927,446, 5,942,712 and 6,545,901. Often, the fitment is in the form of a closure that includes a body or base mounted on the container neck to define a seat for receiving the valve and includes a retaining ring or other structure for holding the valve on the seat in the base. See, for example, U.S. Pat. Nos. 6,269,986 and 6,566,016. The valve is normally closed and can withstand the weight of the fluid product when the container is completely inverted so that the liquid will not leak out unless the container is squeezed. With such a system, the lid or cap need not be re-closed (although it is typically re-closed if the package is to be transported to another location, packed in a suitcase, etc.).
While such valves and valve systems have significant advantages and function well, there is always room for improvement.